Mesencephalon Mesencephalon
(Midbrain) (Midbrain)
Prof. Dr. Selda Önderoğlu
Prof. Dr. Selda Önderoğlu
Mesencephalon Mesencephalon
Shortest part of brain stem
About 2 cm
RELATIONS:
Inf: Pons
Post: Cerebellum
Sup:
Diencephalon
External features-Ventral (ant.) surface External features-Ventral (ant.) surface
Crus cerebri (Cerebral peduncles
Interpeduncular fossa (bw.crus cerebri)
Oculomotor n.
exits from interped.
fossa
Posterior perforated substance: surface of interpeduncular fossa (post. Cereb.
a passes here)
Dorsal
Dorsal
(post) (post)surface surface
Superior colliculus
Inferior colliculus
Brachium of superior colliculus
Brachium of inferior colliculus
cruciform sulcus
Upper limit of sulcus expands into a
depression for pineal gland
From caudal end of the sulcus; a median
frenulum veli is
prolonged down over sup medullary velum Lat to frenulum;
trochlear n. emerges
Dorsal surface
Dorsal surface
Cranial nerves which leave the brain stem at mesencephalon level
1- oculomotor nerve (contains motor and
parasympathetic fibers)
2- trochlear nerve (contains motor fibers)
Trochlear n.
Trochlear n.
Exit from post.
surface of
mesencephalon
The only nerve which exit from beain stem’s post surface
It Passes ventrally over the lat aspects of cerebral
peduncles and
Continues its
course
Internal structure of mesencephalon Internal structure of mesencephalon
Divided into 3 parts
Crus cerebri
Tegmentum
Tectum (lamina tecti)
Crus cerebri+
tegmentum:
Cerebral peduncle
Substantia nigra separates crus cerebri and
tegmentum
Internal structure of mesencephalon
Crus cerebri Crus cerebri
--
2 white matter
structures(axons)
-
Formed by fibers
emerging from cerebral hemispheres
-
They meet each other at the
superior border of pons
Crus cerebri Crus cerebri
Fibers in crus cerbri From medial to lateral:
Frontopontine fibres
Corticonuclear fibres
Corticospinal fibres
Occipitopontine fibres
Parietopontine fibres
Temporopontine fibres
Tegmentum Tegmentum
Between substantia nigra and tectum
Cerebral aqueduct (connects 3rd and 4th ventricles)
Periaqueductal gray
substance (around
cerebral aqueduct)
Tectum Tectum
Posterior to cerebral aqueduct
Structures here:
Superior colliculus
related to auditory reflexes
Inferior colliculus
related to visual
reflexes
Inferior colliculus level Inferior colliculus level
Decussation of superior cerebellar peduncle
Trochlear nucleus
Superior colliculus level Superior colliculus level
Oculomotor nucleus
Red nucleus (nucleus ruber)
Inferior Inferior
colliculus colliculus
Related to Auditory pathway
Lateral lemniscus inferior colliculus brachium of inferior colliculus
medial geniculate body auditory cortex
Localize the voice
Evaluate the frequency of voice
Concentrate the attention to a certain voice
Motor reflexes related to hearing
Substantia nigra Substantia nigra
Located Bw. crus
cerebri and tegmentum
Dark color depend upon to melanin pigment
Formed by :
Pars compacta (dorsal) – Dopaminergic and
cholinergic neurons containing melanin pigment
Pars reticularis (ventral) – GABA-ergic neurons
(mostly) and dopaminergic neurons (few)
Neuron group related to basal ganglia
Substantia nigra (connections) Substantia nigra (connections)
Afferents
– Caudate nucleus – Putamen
– Globus pallidus
– Posterior raphe nucl.
– Pedunculopontine tegmental nucleus
Efferents
– Caudate nucleus – Putamen
– Thalamus
– Superior colliculus – Pedunculopontine
tegmental nucleus
Red nucleus (nucleus ruber) Red nucleus (nucleus ruber)
Part of reticular formation
Dorsomedial to substantia nigra
Observed from caudal levels of superior colliculus to
caudal levels of diencephalon
Parts of red nucleus:
Pars parvocellularis (rostral)
Pars magnocellularis (caudal)
Connections Connections (red nucleus) (red nucleus)
Afferents
– Cerebellar nuclei – Cerebral cortex
(corticorubral fibres)
Efferents
– Cross mid-line in anterior tegmental decussation – Cerebellum
– Brain stem nuclei
– Spinal cord (rubrospinal tract); related to flexor muscle tone
Interpeduncular Interpeduncular
nucleus nucleus
Located at the
Interpeduncular fossa (dorsal)
At the midline
Receive aff fibres from habenular nuclei by fasciculus retroflexus
Eff fibers arise as medial forebrain bundle and
reach to septal nuclei
Superior colliculus Superior colliculus ( ( related to visual pathway) related to visual pathway)
Afferents
– Retina
– Cerebral cortex (corticotectal fibres) – Inferior colliculus
– Spinal cord (spinotectal tract)
– Substantia nigra
Efferents
– Brain stem – Spinal cord – Thalamus
– Nucleus parabigeminalis – Reticular nuclei
– Pretectum – Retina
Efferent fibres of superior colliculus Efferent fibres of superior colliculus
Tectopontine fibres (uncrossed)
cerebellum
Control of head and eye movements
Tectobulbar fibres and Tectospinal fibres cross in posterior tegmental
decussation MLF Related to eye
movements
Posterior commissure Posterior commissure
Contains fibers that cross and course to other
cerebral hemisphere
( one of the commissural pathways)
Also Has nucleus of post commissure
Fibres passing from post comm originate from:
pretectal nuclei,
nucleus of post com,
Cajal’s interstitial nucleus,
sup colliculus,
dorsal thalamic nuclei
Pretectal area Pretectal area
at the level of posterior commissure
Contains Pretectal nuclei (related with visual
pathways)
Reticular nuclei Reticular nuclei
Nucleus cuneiformis
Nucleus
subcuneiformis
Nucleus tegmenti pedunculopontinus
Raphe nuclei:
Nucleus raphes
dorsalis
Cranial n. nuclei Cranial n. nuclei
Parasympathetic nucleus of oculomotor n. (Edinger- Westphal)
Motor nucleus of oculomotor n.
Motor nucleus of trochlear n.
Mesencephalic nucleus of trigeminal n. (GSA)
Nuclei of oculomotor n.
Nuclei of oculomotor n. (cran. N. III) (cran. N. III)
at the level of superior colliculus
Ventral to periaqueductal grey matter
Dorsal to MLF
2 nuclei:
1- P-symp:
Edinger-Westphal nucleus:
Pregang parasymph fibres from E.W. nucleus ciliary gang postgang
parasymph fibres from
ciliary gang i,nnervate m.
sphincter pupilla, m. Ciliaris 2- Motor nucl.of III: Rectus sup, inf, medialis, obl inf, levator palpebra sup
Motor nucleus of trochlear n. (cran. N.
Motor nucleus of trochlear n. (cran. N.
IV) IV)
In the upper levels of inf colliculus
Ventral to periaqueductal grey matter
Axons decussate in sup medullary velum
motor fibres to Obliquus sup m. (eye)
Mesencephalic nucleus of V Mesencephalic nucleus of V
Lat to periaqueductal grey matter
Extends from upper levels of pons to sup colliculus level
Aff fibres of this nucleus carry proprioceptive
impulses from teeth,
periodontium, hard palate, mm. of mastication, joint capsules
